<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <meta name="viewport" content="width=device-width,initial-scale=1">
    <style>
    .box{
        width: 200px;
        height: 200px;
        transition: 2s;
        background-color:red;
    }
    .box:hover{
        opacity: 0;;
    }
    
    </style>
</head>
<body>
    <div class="box">
        
    </div>
</body>
</html>